Optical recording medium and production process for the medium

ABSTRACT

An optical information recording medium is provided in which the active layer is a phase change material capable of absorbing energy and being converted between a substantially amorphous state and a substantially crystalline state. The active layer contains nitrogen, which may be in the form of a nitride or nitrides of the constituent elements of the active layer, or may be a nitrided surface thereof. The inclusion of nitrogen inhibits localized shifting of the active material, which leads to degradation of the recording/erase properties of the medium. The optical recording medium includes a substrate, onto which is deposited in sequence a first dielectric layer, a nitrogen-containing active layer, a second dielectric layer, and a metallic reflecting layer. The second dielectric layer is made thin, so that the cooling rate of the active layer is increased to form a more uniform amorphous state.

The present invention relates to an optical information storage mediumhaving a large memory capacity in which the temperature or an activerecording layer is controllably elevated by optical irradiation, therebyusing structural phase changes or atomic rearrangements in the activelayer by which the information is either recorded or erased.

BACKGROUND OF THE INVENTION

Optical recording discs in the prior art include non-erasable write-oncesystems which utilize as the active recording layer a TeO_(x) (0<x<2.0)thin film formed from Te and TeO₂. Erasable discs have also beenreported and are being developed for practical applications in which itis possible to repeatedly write and erase information by optical means.In such erasable optical discs, a thin film layer of material istypically heated and melted by laser light, then rapidly cooled so thatits structure is in a substantially non-crystalline or amorphous state,thereby recording information which is indicated by the opticalproperties of the substantially non-crystalline or amorphous state. Therecorded information can be subsequently erased by heating the activelayer, and then slowly cooling it so that its atomic structure annealsand transforms into a substantially crystalline state, having differentoptical properties from that of the amorphous state, which indicatethereby an erased condition.

Materials investigated as active layers for erasable discs which operatevia a phase change mechanism involving an amorphous/crystallinetransition include various combinations of the chalcogen elements asexemplified by Ge₁₅ Te₈₁ Sb₂ S₂. Such combinations have been studied byOvshinsky et. al and Feinleib et al. (see Appl. Phys. Lett., vol. 18(1971)). In addition, thin film active layers consisting of combinationsof a chalcogen element or elements with an element or elements chosenfrom Group V of the periodic table or an element or elements chosen fromGroup IV of the periodic table, e.g. Ge, As₂ S₃, As₂ Se₃ or Sb₂ Se₃ areknown and have been studied in the prior art.

It is possible to produce an optical disc having thin film active layerson a substrate in which grooves are formed for the purpose of guidingthe laser light. With respect to the utilization of such optical discfor the recording and erasing of information by laser light, the activelayer is generally crystallized in advance, and a laser beam focused toa spot size of about 1 micron is intensity modulated between a peakpower level and a lower bias power level with the recorded information.For example, a circular recording disk may be rotated and irradiatedduring rotation with pulses of laser light having a peak powersufficient to increase the temperature of the irradiated areas on theactive layer above the melting point of the layer. If the irradiatedareas are permitted to cool rapidly, the information will be recorded bythe formation of substantially non-crystalline or amorphous marks at thelocations of the irradiated areas.

Amorphous areas of the disc which are irradiated with the lower biaspower level of the laser light can have the temperature in those areaselevated above the crystallization temperature of the active layer, inwhich case the active layer at those irradiated areas will betransformed back into a substantially crystalline structure, and therecorded information will thereby be erased, making it possible toover-write information. In this manner, areas on the active layer may berepeatedly cycled above the melting point thereof to produce recordedamorphous areas, or above the crystallization temperature thereof toproduce crystalline erased areas, thereby effectuating the recording oroverwriting of binary information.

Typically, the active layer in an optical disc is sandwiched betweendielectric layers which have excellent heat resistance characteristics.These dielectric layers serve to contain the active layer and to protecta substrate and an adhesive layer from undergoing large changes intemperature during irradiation. Since the thermal behavior of the activelayer, both as to it its ability to rapidly increase in temperature, aswell as its rapid cooling and slow, cooling characteristics, depend onthe thermal conductivity of these dielectric layers, it is possible tooptimize the recording and erasing characteristics by properly choosingthe materials of the dielectric layers and by carefully controlling thethickness and composition of these layers.

Important design parameters which must be considered in developing andoptimizing an erasable over-write optical recording medium are theerasability of the medium and the cyclability of the recording anderasing characteristics over many write/erase cycles.

With regard to the cyclability characteristics, studies have shown thatthere is a deterioration after a large number of write/erase cycleswhich results from thermal damage to the disc substrate or protectivelayer and which is manifested as an increase in noise. Further, studieshave also shown that even in the absence of such thermal damage, a shiftor physical distortion of the active layer along the direction ofrotation of the disc may occur after many write/erase cycles as a resultof thermally induced stress and distortion of the protective dielectriclayers induced by the repeated heating and cooling cycles (see SPIEOpitcal Data Storage Topical Meeting, vol. 1078, p.27, Ohta et al.).

With regard to the erase characteristics, the melting point ofnon-crystalline films containing Te typically covers a wide temperaturerange of 400° C. to 900° C. As explained above, crystallization may beachieved by irradiating the active layer with laser light to increaseits temperature, followed by a gradual cooling. The required temperatureis generally within a range close to the crystallization temperature ofthe material, which is less that the melting point. When thecrystallized film is irradiated with laser light having a higher powerand is heated above the melting point, the film, upon rapid cool down,becomes substantially non-crystalline or amorphous, and an opticallydetectable mark is formed.

If the amorphous state is selected to represent the recorded condition,it is known that a more rapid cooling results in a more uniformamorphous state and results in a mark which produces a better and morestable signal. (See "Phase Change Disk Media Having Rapid CoolingStructure", Ohta et al., Jap. J. Appl. Phys. vol 28, 123 (1989)). Thesestudies have shown that when the rate of cooling is too low, therearises a difference in the degree of non-crystallinity between thecenter of the mark and the periphery of the mark. During erasure, themark is recrystallized. If the recorded mark is non-uniform instructure, the crystallization which occurs during subsequent erasurewill be rendered non-uniform as well, resulting in a recording mediumwith less than optimum erasure characteristics.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved opticalrecording medium having an active recording thin film layer which can berendered substantially non-crystalline or amorphous upon absorption oflaser light energy, whereby a melting and rapid cooling of the activelayer is produced, and which can be rendered substantially crystallineby heating the amorphous layer above the crystallization temperature.

It is a further object of the present invention to provide an erasableoptical information recording medium with improved over-writecyclability characteristics and improved laser power dependencecharacteristics.

It is yet a further object of the present invention to provide anoptical recording medium which has improved thermal characteristics, andimproved long term stability with respect to thermal stress anddeterioration induced by many write/erase cycles.

A still further object of the present invention is to provide a processfor manufacture of an erasable optical information recording mediumhaving such improved characteristics.

Accordingly, there is provided an optical recording medium having anactive layer which is capable of absorbing energy and being convertedbetween a substantially non-crystalline amorphous state and asubstantially crystalline state, wherein the active layer includesnitrogen. The optical recording medium generally comprises a structurewhich includes a substrate, a first dielectric layer formed on onesurface of the substrate, an active layer formed on top of the firstdielectric layer wherein the active layer includes nitrogen, a seconddielectric layer formed on top of the active layer, and a reflectinglayer formed on top of the second dielectric layer. The active layer maybe formed by incorporation of nitrogen into a chalcogenide compositionof Ge, Te, and Sb The nitrogen may be incorporated as a nitride of oneof the chalcogen elements, or may form a nitrided surface layer on thechalcogen composition. The active layer may be produced by sputtering atarget in a nitrogen containing rare gas mixture, or by sputtering atarget which includes a nitride composition.

As explained, one of the factors which contributes to the deteriorationof the recording and erasing characteristics after many write/erasecycles is a localized shift of the material in the active layer. Toprevent or reduce the tendency for this shift to occur, in the presentinvention, nitrogen or a nitride substance is incorporated in the activelayer or on its surface.

Furthermore, the optical recording medium which incorporates this activerecording layer sandwiches the recording layer between a firstdielectric layer formed on one side of a transparent substrate, and asecond dielectric layer. The second dielectric layer has a metallicreflecting layer formed on the other side thereof. By making the filmthickness of the second dielectric layer thinner than that of the firstdielectric layer, the metallic reflecting layer is thereby placed closerto the active recording layer, and is able to more rapidly dissipate theheat generated in the active layer by the laser light. This permits arapid cool down to occur and a highly uniform amorphous mark to beproduced. The high uniformity of the amorphous mark is desirable foroptimizing the erase characteristics of the material.

The above mentioned composition of the recording layer and overallstructure of the optical recording medium therefore inhibits the meltshifting which is known to occur in recording layers having othercompositions, and results in structure in which the long termcyclability and stability of the record/erase characteristics and powerdependency of the laser light is improved over the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding the nature, features and advantages of thepresent invention, reference should be made to the following detaileddescription of various preferred, but nonetheless illustrativeembodiments of the invention, as illustrated by and taken in conjunctionwith the accompanying drawings wherein:

FIG. 1 is a cross sectional view which shows the structure of an opticalinformation recording medium in accordance with the first and secondembodiments of the invention.

FIG. 2 is a cross sectional view which shows the structure of an opticalinformation recording medium in accordance with a third embodiment ofthe present invention.

FIG. 3 is a cross sectional view which shows the structure of an opticalinformation recording medium in accordance with yet another embodimentof the present invention.

FIG. 4 is a triangular composition diagram showing the preferredcomposition of the active layer of one embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1, there is shown a cross sectional view of anoptical recording medium which includes a disc substrate 1 which may bea resin substrate formed from poly-carbonate or other similar material.The disc substrate 1 may have grooves preformed therein for guiding thelaser light, which is shown as incident on the disc in the direction ofthe arrow denoted by reference numeral 8. Alternatively disc substrate 1may be a glass plate formed by the 2P process, a substrate prepared bydirectly forming grooves on a glass plate, or a substrate on which bitrows for guiding laser light have been preformed thereon.

As shown in FIG. 1, a first dielectric layer 2 of approximately 160 nmin thickness, which may consist of a mixed film of ZnS and SiO₂, isformed on top of disc substrate 1. The first dielectric layer 2 hasdeposited thereon an active layer 3 having a thickness of approximately20-30 nm, in which nitrogen is incorporated into a composition ofTe-Ge-Sb. A second dielectric layer 4 covers the active, recording layer3. The second dielectric layer 4 may be of the same composition as thefirst dielectric layer 2, but has a thickness of only approximately 20nm. Covering the top of the second dielectric layer 4 is a reflectinglayer 5 which may be an Al alloy. Finally, to complete the structure, aprotective plate 7 is adhered to the top of the reflective layer 5 bymeans of an adhesive layer 6. Protective plate 7 may be another disc,and in such case top and bottom surfaces of the optical recording mediumare discs.

In the structure shown in FIG. 1, the laser light for recording,erasing, and reproducing the information contained therein is incidentin the direction shown by arrow 8, and has an intensity which ismodulated with the information. Detection of the recorded informationmay be performed by detecting the reflected light.

To produce the two dielectric layers 2,4, the active layer 3, andreflecting layer 5, a vacuum deposition or embodiment of the activelayer 3, for example, a sputtering process may be used in whichsputtering is performed in a mixture of a rare gas such as argon andnitrogen gas. During such sputter deposition, the partial pressure ofnitrogen in the gas is an important process parameter which determinesthe characteristics and quality of the active layer 3. During sputteringof the active layer 3, an appropriate range for the partial pressure ofnitrogen is 1.0×10³¹⁵ Torr to 1.0×10⁻⁴ Torr. If the nitrogen partialpressure is less than approximately 10⁻⁵ Torr, then the effect ofnitrogen during sputtering becomes small, and consequently theimprovement of the cyclability characteristics as a result of theinclusion of nitrogen in the Te-Ge-Sb active layer structure becomessmall. On the other hand, if the partial pressure of nitrogen duringsputtering is greater than about 10⁻⁴ Torr, the optical characteristicsof the active layer 3, such as the refractive index are affected, andthe basic recording and erasing characteristics of the active layer 3,such as the speed of crystallization and non-crystallization move awayfrom their optimum range. Accordingly, the above-mentioned range for thepartial pressure of nitrogen during sputter deposition is mostappropriate.

With respect to the first dielectric layer 2 and the second dielectriclayer 4, the mixing ratio of ZnS and SiO₂ is generally selected so thatthe SiO, comprises 20 mol % of the overall composition. The compositionneed not, however, be so limited. However, if the SiO₂, is less thanabout 5 mol %, the effect of SiO₂, on the mixture, i.e. to reduce thediameter of the crystal particles, is diminished. On the other hand, ifthe concentration of SiO₂, is above 50 mol %, then the properties of thefilm degrade. Therefore, it is appropriate to keep the ratio of SiO₂ inthe range of 5 to 40 mol %.

The thickness of the second dielectric layer 4 is made as thin as about20 nm, so that the reflecting layer 5, which also acts as a thermaldissipation layer, is placed closer to the active layer 3. Thus the heatfrom the active layer 3 generated by the laser beam during recording anderasing may be rapidly conducted to the reflecting layer 5, producing arapid cooling of the active layer 3 which results in a more uniformamorphous record mark.

Experiments have been performed on the disc structure of the firstpreferred embodiment of the invention as described above, in which theover-write characteristics of a signal of frequency f1=3.43 MHz and asignal of frequency f2=1.25 MHz were measured at an outer diameter of130 mm, on a disc rotating at 1800 rpm, which corresponds to a linearspeed of 8 m/sec. The over-write was carried out by a method ofsimultaneously recording and erasing, in which a substantiallynon-crystalline record mark was formed by irradiation at a high laserpower level or 16 mw, and then crystallized by irradiation at a lowlaser power level of 8 mw, with a circular laser spot of about 1 micronin diameter.

As a result of these measurements, a C/N ratio for the recorded signalof 55 db or greater was obtained, with an erasability of greater than 30db. With respect to repetitive cycling, the bit error rates weremeasured, with no deterioration observed for over one million cycles.

As a second preferred embodiment, a recording layer is made of achalcogen which contains a nitride/nitrides of at least one elementselected from Te, Ge, and Sb. The optical recording medium consists of asubstrate, and a 4-layer structure having a first dielectric layer, anactive layer, a second dielectric layer, and a reflecting layer,configured as generally shown in FIG. 1. In this second embodiment, theactive layer 3 contains a nitride/nitrides or an oxide/oxides of atleast one element selected from Ge, Te, and Sb, and has a film thicknessof about 20-30 nm.

To form the structure of the second preferred embodiment, a sputterdeposition process or an electron beam evaporation process may be used.For sputter deposition, it is possible to fabricate a sputter targetwhich contains a nitride/nitrides or Ge, Te, or Sb. With such target, itis possible to carry out the sputter deposition with only argon (Ar)gas. It is also Possible to allow the above-mentioned nitride/nitridesto be contained in a deposition source for use in electron beamevaporation.

The disc structure of this second preferred embodiment was studied byinvestigating the over-write characteristics using a signal of frequencyf1=3.43 MHz and a signal of frequency f2=1.25 MHz applied at an outerdiameter of 130 mm to a disc rotating at 1800 rpm, which corresponds toa linear speed of 8 m/sec. The over-write was carried out by a method ofsimultaneously recording and erasing, in which a substantiallynon-crystalline record mark was formed by irradiation at a high laserpower level of 16 mw, and then crystallized by irradiation at a lowlaser power level of 8 mw, with a circular laser spot of about 1 micronin diameter.

As a result of these measurements, a C/N ratio for the recorded signalof 55 db or greater was obtained, with an erasability of greater than 30db. With respect to repetitive cycling, the measurement of bit errorrates showed no deterioration after more than one million cycles.

A third embodiment of the instant invention is now explained withreference to FIG. 2, wherein a disc substrate 9 is shown which may be aresin substrate on which grooves for guiding the laser light arepreformed, a glass plate formed by the 2P process, a substrate preparedby directly forming grooves on a glass plate, or a substrate on whichbit rows for guiding the laser light are provided thereon. Deposited ondisc substrate 9 is a first dielectric layer 10, which may consist of amixed film of ZnS and SiO₂. An active layer 11 is then deposited on topof the first dielectric layer 10. The active layer 11 is prepared byallowing a component consisting of a Te-Ge-Sb composition to bedispersed in a matrix of a nitride/nitrides or an oxide/oxides of atleast one element chosen from Te, Ge and Sb. The film thickness ofactive layer 11 is in the range of approximately 20-120 nm. Covering theactive layer 11 is a second dielectric layer 12, made from the samematerial as the first dielectric layer 10, which is deposited to athickness of about 20 nm. A reflecting layer 13 of Al alloy covers thethin second dielectric layer 12. A protective plate 15 is adhered to thetop of the structure by an adhesive layer 14.

In this third embodiment, the light absorption coefficient and filmthickness of the active layer 11 are chosen in such a manner that incomparison with the first and second embodiments described above, thelight absorption coefficient is small, and the film thickness of therecording layer 11 is thicker. When subjected to similar test conditionsas described with respect to the first and second embodiments, the C/Nratio of the recorded signal was found to be 55 db or greater, with anerasability of 30 db or greater. As to the effects of repeatedwrite/erase cycling of the medium, the bit error rates were measured,and no deterioration was observed for more than one million cycles.

A fourth embodiment of the invention is shown in FIG. 3. As showntherein, the optical recording medium may contain a disc substrate 16,which may be a resin substrate formed from poly-carbonate or othersimilar materials. Disc substrate 16 may have grooves preformed thereinfor guiding the laser light, shown as being incident in the direction ofthe arrow denoted by reference numeral 25. Alternatively, disc substrate16 may be a glass plate formed by the 2P process, a substrate preparedby directly forming grooves on a glass plate, or a substrate on whichbit rows for guiding laser light have been preformed thereon.

A first dielectric layer 17, which consists of a mixed film of Zn andSiO₂ having a film thickness of approximately 160 nm is deposited on topof the disc substrate 16. The next layer is an active layer 18, whichhas a Te-Ge-Sb ternary alloy composition as a component thereof, and anitride/nitrides of at least one of the elements Ge, Te, or Sb, or anadsorption surface layer 20 of nitrogen provided on at least one surfaceof the active layer 18. A second dielectric layer 21, made from the samematerial as the first dielectric layer 17, and having a thickness of 20nm covers the active layer 18. A reflecting layer 22 of Al alloy, havinga thickness of about 120 nm covers the second dielectric layer 21. Tocomplete the structure, a protective plate 24 is adhered to thereflecting layer 22 by an adhesive material layer 23.

Experimental measurements performed on this structure, using theparameters described above with respect to the aforementionedembodiments, resulted in a C/N ratio for the recorded signal of 55 db orgreater, and an erasability of 30 db or greater. Further, nodeterioration was found in the write/erase characteristics after morethan one million write/erase cycles.

In a preferred embodiment of this invention, an active recording layeris made from a material which incorporates nitrogen in a Ge, Te and Sbcomposition. It is especially effective to incorporate nitrogen in acomposition range shown in the triangle diagram of FIG. 4, whichrepresents the compositions of the ternary alloy system GeTe-Sb₂ Te₃-Sb. With such a composition, it is possible to obtain stablecharacteristics above one million cycles by appropriately selecting thelaser power for recording and erasing. Furthermore, in addition toobtaining improved stability characteristics beyond one millionwrite/erase cycles over a wide range of laser power, it is also possibleto improve the recording sensitivity of the active layer by permittingthe layer to contain nitrogen or by allowing it to contain anitride/nitrides of at least one element of Ge, Te and Sb. If b=Sb/Sb₂Te₃ (denoting the mole ratio of these two constituents), then anespecially effective composition range for the active recording layer is0<b<1.0. If b is too small, then the effect of the Te component maybecome excessive, and render the active layer poor with respect tooxidation resistance. On the other hand, if b>1.0, then the speed oferasure is reduced. Furthermore, if g=GeTe/Sb₂ Te₃ (mole ratio), thenthe composition range of 0.5<g<3.0 is preferable. If g is 0.5 or less,the thermal resistance stability is reduced, whereas if g is 3.0 orgreater, the sensitivity of the recording layer is reduced, even thoughthe thermal stability remains good.

For the preparation of these layers, a vacuum deposition process or asputter process may generally be utilized. When sputtering is used toprepare this embodiment of the invention, the sputtering may beperformed in a mixture of a rare gas such as argon and nitrogen gas. Asexplained above, during sputter deposition, the partial pressure ofnitrogen in the gas is an important process parameter which determinesthe characteristics and quality of the active layer. During sputteringof the active layer, an appropriate range for the partial pressure ofnitrogen is 1.0×10⁻⁵ Torr to 1.0⁻⁴ Torr. If the nitrogen partialpressure is less than approximately 10⁻⁵ Torr, then the effect ofnitrogen during sputtering becomes small, and consequently theimprovement of the repeatability characteristics as a result of theinclusion of nitrogen in the Te-Ge-Sb active layer structure becomessmall. On the other hand, if the partial pressure of nitrogen duringsputtering is greater than about 10⁻⁴ Torr, the optical characteristicsof the active layer, such as the refractive index is affected, and thebasic recording and erasing characteristics of the active layer 18, suchas the rate of crystallization and non-crystallization, may be adverselyaffected. Accordingly, the above-mentioned range for the partialpressure of nitrogen during sputter deposition is optimum.

Experiments have been performed on the disc structure of this preferredembodiment of the invention, in which the over-write characteristics ofa signal of frequency f1=3.43 MHz and a signal of frequency f2=1.25 MHzwere measured at an outer diameter of 130 mm, on a disc rotating at 1800rpm, which corresponds to a linear speed of 8 m/sec. The over-write wascarried out by a method of simultaneously recording and erasing, inwhich a substantially amorphous record mark was formed by irradiation ata high laser power level of 16 mw, and then crystallized by irradiationat a low laser power level of 8 mw, with a circular laser spot of about1 micron in diameter.

As a result of these measurements, a C/N ratio for the recorded signalof 55 db or greater was obtained, with an over-write erasability of 30db or greater. With respect to repetitive cycling, the characteristicsof bit error rates were measured, with no deterioration observed forover one million cycles.

Although the invention disclosed herein as been described with referenceto particular embodiments, it is to be understood that these embodimentsare merely illustrative of the different aspects and features of theinvention. As such, persons skilled in the art may make numerousmodifications to the illustrative embodiments described herein, andother arrangement may be devised to implement the disclosed inventionwhich will fall within the spirit and scope of the invention describedand claimed herein.

We claim:
 1. An optical recording medium having a recording layercapable of absorbing energy and being converted between a substantiallynon-crystalline state and a substantially crystalline state, whereinsaid recording layer comprises a ternary alloy of Te-Ge-Sb and at leastone nitride or Te, Ge, or Sb.
 2. An optical recording mediumcomprising:a) a substrate; b) a first dielectric layer formed on onesurface of said substrate; c) a recording layer formed on said firstdielectric layer, said recording layer capable of absorbing energy andbeing converted between a substantially non-crystalline state and asubstantially crystalline state, wherein said recording layer includes aternary alloy of Te-Ge-Sb and at least one nitride of Te, Ge, or Sb; d)a second dielectric layer formed on said recording layer having athickness substantially less than the thickness of said first dielectriclayer; and e) a reflecting layer formed on said second dielectric layer.3. An optical recording medium in accordance with claim 2, wherein saidsecond dielectric layer has a thickness of 30 nm or less.
 4. An opticalrecording medium in accordance with claim 2, wherein said first andsecond dielectric layers comprise a mixture of ZnS and SiO₂ in whichSiO₂ is n a concentration range of 5-40 mol %.
 5. An optical recordingmedium comprising a recording layer which includes a ternary alloy orTe-Ge-Sb and at least one nitride of Te, Ge or Sb.
 6. An opticalrecording medium comprising:a) a substrate; b) a first dielectric layerformed on one surface of said substrate; c) a recording layer formed onsaid first dielectric layer, said recording layer capable of absorbingenergy and being converted between a substantially non-crystalline stateand a substantially crystalline state, wherein said recording layerincludes a ternary alloy or Ge-Te-Sb and germanium nitride; d) a seconddielectric layer formed on said recording layer having a thicknesssubstantially less than the thickness of said first dielectric layer;and e) a reflecting layer formed on said second dielectric layer.
 7. Anoptical recording medium in accordance with claim 6, wherein said seconddielectric layer has a thickness of 30 nm or less.
 8. An opticalrecording medium in accordance with claim 6, wherein said first andsecond dielectric layers comprise a mixture of ZnS and SiO₂ in whichSiO₂ is in a concentration range of 5-40 mol %.
 9. An optical recordingmedium comprising a recording layer which includes a ternary alloy ofTe-Ge-Sb dispersed in a matrix selected from the group consisting of Tenitride, Ge nitride and Sb nitride.
 10. An optical recording mediumhaving a recording layer comprising a ternary alloy composition of Sb,Sb₂ Te₃, and GeTe, said composition further including at least onenitride of Ge, Te, or Sb.
 11. An optical recording medium in accordancewith claim 10, wherein the mole ratio of GeTe to Sb₂ Te₃ is greater than0.5 and less than 3.0.
 12. An optical recording medium comprising:a) asubstrate; b) a first dielectric layer formed on one surface of saidsubstrate; c) a recording layer formed on said first dielectric layer,said recording layer capable of absorbing energy and being convertedbetween a substantially non-crystalline state and a substantiallycrystalline state, wherein said recording layer includes a ternary alloyof GeTe, Sb₂ Te₃, Sb and at least one nitride of Ge, Te, or Sb; d) asecond dielectric layer formed on said recording layer having athickness substantially less than the thickness of said first dielectriclayer; and e) a reflecting layer formed on said second dielectric layer.13. An optical recording medium in accordance with claim 12, whereinsaid second dielectric layer has a thickness which is 30 nm or less. 14.An optical recording medium in accordance with claim 12, wherein saidfirst and second dielectric layers comprise a mixture of ZnS and SiO₂ inwhich SiO₂ is in a concentration range of 5-40 mol %.
 15. An opticalrecording medium in accordance with claim 12, wherein the mole ratio ofGeTe to Sb₂ Te₃ is greater than 0.5 and less than 3.0. .Iadd.
 16. Theoptical recording medium of claim 1, wherein said at least one nitrideof Te, Ge or Sb is present only as a nitrided surface layer formed as atleast one surface of said recording layer. .Iaddend..Iadd.17. Theoptical recording medium of claim 2, wherein said at least one nitrideof Te, Ge or Sb is present only as a nitrided surface layer formed as atleast one surface of said recording layer. .Iaddend..Iadd.18. Theoptical recording medium of claim 1, wherein at least one surface ofsaid recording layer includes said at least one nitride of Te, Ge or Sb..Iaddend..Iadd.19. The optical recording medium of claim 2, wherein atleast one surface of said recording layer includes said at least onenitride of Te, Ge or Sb. .Iaddend.